An image sensor may be a semiconductor device that may convert optical images into electric signals, and may be mainly classified into a charge coupled device (CCD) image sensor and a CMOS image sensor.
Such an image sensor may include a photodiode that may detect light. The image sensor may further include a logic circuit that may convert detected light into electric signals. The detected light may thereby be represented as data. As an amount of light received in the photodiode increases, the photo sensitivity of the image sensor may improve.
Photo sensitivity may be improved by various methods. For example, a fill factor, which may be a ratio of a photodiode area to the whole area of the image sensor, may be increased. Alternatively, photo-gathering technology may be used to change a path of light incident onto an area other than the photodiode area such that the light may be gathered in the photodiode.
A micro-lens is an example of the photo-gathering technology. For example, a convex micro-lens may be formed on a top surface of a photodiode. The micro-lens may be formed using a material having superior light transmittance. The micro-lens may refract a path of incident light in such a manner that a greater amount of light may be transmitted into the photo-diode area. Hence, light parallel to an optical axis of the micro-lens may be refracted by the micro-lens, and light may be focused at a specific position on the optical axis.
A related art image sensor may include various components, such as a photodiode, an interlayer dielectric layer, a color filter, a micro-lens, and so on.
An interlayer dielectric layer may be formed on a semiconductor substrate formed with a plurality of photodiodes. RGB color filter layers may be formed on the interlayer dielectric layer and may correspond (i.e. be aligned) with the photodiodes, respectively.
A planar layer may be formed on the color filter layers and may planarize an irregular surface that may occur on the color filter layers. In addition, micro-lenses may be formed on the planar layer to correspond with the photodiodes and the color filter layers, respectively.
The photodiode may detect light and may convert the light into an electric signal. The interlayer dielectric layer may insulate metal interconnections from each other. The color filter may exhibit the three primary colors of red, green, and blue (R, G, B). The micro-lens may guide the light onto the photodiode.
FIGS. 1A to 1D illustrate a related art method of manufacturing a micro-lens.
Referring to FIG. 1A, micro-lens layer 52 may be formed on semiconductor substrate 10 on which a plurality of photodiodes 40, interlayer dielectric layer 20, a color filter layer 30, and planar layer 25 may be formed.
Referring to FIG. 1B, micro-lens layer 52 may be patterned such that a micro-lens pattern may correspond to locations of to photodiodes 40.
Referring to FIG. 1C, semiconductor substrate 10 may be loaded on hot plate 60 and heat may be applied to semiconductor substrate 10. Accordingly, the micro-lens may be formed.
Referring to FIG. 1D, as illustrated in portions A and B, micro-lens 50 of the image sensor manufactured through the related art method may have an irregular surface.
If heat is directly applied to semiconductor substrate 10, which may be formed with micro-lens layer 52 and may be loaded on hot plate 60, the heat transfer coefficient or heat capacity may be locally uneven depending on the heat transfer route formed below micro-lens layer 52, or the heat transfer rate may be locally uneven due to the step difference. This may result in irregular heat transfer may occur, which may cause micro-lens 50 to have an irregular surface.
That is, adjacent micro-lenses 50 may be bonded to each other (see, A of FIG. 1D), or a curvature surface of micro-lens 50 may be distorted or crushed (see, B of FIG. 1D). This may negatively affect pixels adjacent to micro-lens 50 and may degrade a focusing efficiency of a micro-lens.